This invention relates to a transducer for converting mechanical forces into corresponding electrical signals, and in a preferred embodiment, it relates to a writing instrument and system capable of recording repeatable characteristics involved in an individual's signature or writing for use in automated user verification systems.
Recently, there has been an increasing trend towards using a record medium like a "credit card" in various business transactions. These transactions include the use of credit verification machines for credit purchases and automated banking teller machines, which among other transactions, include the dispensing of cash.
With an increasing reliance on the use of a "credit card" in business transactions, it is increasingly important to develop a commercially feasible system for verifying the identity of the person using the credit card. Some of the prior art user verification systems include the use of secret code numbers which are manually entered on a business machine like an automated banking teller machine, and signature verification systems.
Some of the prior art signature verification systems are shown in the following U.S. patents:
U.s. pat. No. 3,528,295 which issued Sept. 15, 1970 PA1 U.s. pat. No. 3,579,186 which issued May 18, 1971 PA1 U.s. pat. No. 3,618,019 which issued Nov. 2, 1971 and PA1 U.s. pat. No. 3,621,720 which issued Nov. 23, 1971.
In general such signature verification systems include a writing instrument having a force transducer associated therewith for producing a substantially continuous time-varying electrical signal which is correlated to the varying force which an individual produces with the instrument during a normal writing process. Each individual appears to have a definite, repeatable pressure pattern for signing his name, for example, and such pressure patterns can be utilized in such systems for identification of the user of a "credit card" when it is presented for use by having the user sign his name with the writing instrument and by comparing the user's current pressure pattern with what has been previously recorded by him.
One prior art writing instrument utilizes a strain gauge for converting the pressure variations between a stylus included therein and a writing surface during the act of writing into electrical signals which correspond to the pressure variations.
One of the problems with a writing instrument which utilizes a strain gauge for converting the pressure variations into electrical signals is that the strain gauge is very susceptible to damage. If the writing instrument is to be used in a user identification system associated with an automated teller machine, for example, it may be dropped by a user or subject to vandalism, as these machines are often left unattended. Another problem with a strain gauge type writing instrument is that it is also temperature dependent. Because an automated teller machine, for example, may be installed in an outdoor open area and consequently be exposed to varying climate and temperature conditions, a strain-gauge type writing instrument used therewith would also be subjected to such varying conditions, making its output somewhat unreliable.
Another prior art writing instrument utilizes a differential transformer with a moveable core for converting the pressure patterns formed during the process of writing into corresponding electrical signals. This writing instrument is also expensive to produce, susceptible to damage, and may be susceptiable to outside magnetic radiations or influence.
In contrast with the above, the transducer means of the present invention is very rugged, inexpensive to produce, provides sensitive readings, and is relatively immune to outside magnetic radiation or an unfavorable outdoor environment.